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Giant US telco AT&T has patented a technique for bypassing a certain kind of spam filter.

Patent 6,643,686, granted on November 4 2003 and filed four years ago, details a "system and method for counteracting message filtering", which covers:

A system and method for circumventing schemes that use duplication detection to detect and block unsolicited e-mail (spam). An address on a list is assigned to one of m sublists, where m is an integer that is greater than one. A set of m different messages are created. A different message from the set of m different messages is sent to the addresses on each sublist. In this way, spam countermeasures based upon duplicate detection schemes are foiled.

The author of the patent, AT&T's Robert J Hall, has written a number of papers on computer security. The patent was highlighted by the Internet Patent News newsletter.

Five years ago, some unprincipled ISPs, including UUNet UK, saw spam as a means to boost traffic over their networks and therefore revenue.

SiliconValley.com's Dan Gillmor speculates that AT&T might have nobler motives. By patenting techniques for bypassing spam filters, AT&T can sue spammers for using such techniques; but he rejects this idea on the grounds that spammers are hardly going to throw in the towel because of a little legal difficulty.

A UK representative of AT&T said that it was united with the rest of the industry in supporting attempts to clamp down on unsolicited bulk email. Spam causes huge problems of its network, he added.

The spokesman couldn't comment on the specifics of the patent but offered to pass our query onto his US colleagues in AT&T's research labs. We await their response with interest. ®